The present invention relates to an exercise device having an endless surface, and more particularly to a treadmill having a motor driven endless belt with the capability of automatically changing the speed of the belt in accordance with the position of a user relative to the treadmill.
Treadmills are usually motor driven with the speed of the belt being adjustable by a user reaching forward and pressing correct buttons on a console. However, running on a treadmill, especially at speeds in excess of 8 miles per hour, requires an extra amount of coordination when adjusting the speed on the console, as it is difficult to adjust the speed on the console without breaking stride or falling. Therefore, a workout on a treadmill can be made safer and more effective by automatically controlling the speed of the belt.
Motor driven treadmills which do not require the user to manually adjust a control knob to adjust the belt speed can be categorized into two types. The first type adjusts the belt speed as a function of a user's biological functions and the second type adjusts the belt speed as a function of a user's position relative to the treadmill.
The most common variety of the first type automatically controls the belt speed as a function of a user's heart rate. One such device is U.S. Pat. No. 3,518,985 to Quinton, providing an electrocardiograph pickup device attached to the user detecting the user's heart rate, and a controller adjusting the belt speed to keep the user's heart rate to a predetermined selected value. While treadmills of this type of control system may be preferred for heart patients, many users prefer to run on treadmills which are more performance oriented as opposed to health oriented.
Treadmills of the second type, which automatically control the belt speed in accordance with the position of the user, are desirable because they permit the user to adjust the belt speed by merely changing their pace, thus simulating natural conditions more closely. French Patent 1,565,617, U.S. Pat. No. 1,919,627 issued to Fitzgerald, and U.S. Pat. No. 4,708,337 issued to Shyu are three examples of devices which fall within this second type.
French Patent 1,565,617 discloses a motor driven treadmill having sensors placed at the sides of the treadmill of sensing the position of the user. There are five sensors arranged from the front to the rear of the treadmill. Each sensor consists of an incandescent lamp and photoelectric cell. The sensors feed signals to an electric circuit controlling the motor which drives the treadmill belt. The sensor closest to the rear of the treadmill turns the motor on and sensor closest to the front of the treadmill turns the motor off. The three sensors in the middle make it possible to increase or reduce the speed of the motor in accordance with the sensed position of the user.
U.S. Pat. No. 1,919,627 issued to Fitzgerald provides a motor driven treadmill automatically controlled by the position of the user's body with respect to an electrostatic sensor fixedly mounted to the treadmill. The sensor is an arrangement of capacity plates or electrodes located at the forward end of the treadmill and senses the location of the user by being electrically influenced due to electrical capacity of the user's body.
U.S. Pat. No. 4,708,337 issued to Shyu discloses a motor driven treadmill wherein the belt is driven by a motor automatically controlled by the position of the user's body. The position of the user's body is sensed by an ultrasound sensor mounted on the control panel. The speed of the drive motor is adjusted as a function of the position of the user as sensed by the ultrasound sensor.
Although the above-described treadmills automatically increase and decrease the belt speed as a function of the position of a user, they include disadvantages which make them more susceptible to damage and less accurate.
The location of the sensors for each above-described treadmill which sensing the position of a user are located above the belt surface, the photoelectric sensors are mounted on side rails and the electrostatic and ultrasound sensors being mounted on the front console. As these sensors are mounted in areas which can be contacted, they are susceptible to damage by being bumped or struck by objects and persons, causing malfunctions in the treadmill. Additionally, many of these sensor arrangements may be cost prohibitive to implement on treadmills in today's marketplace.
The sensors for each of the treadmills are also less accurate than many users desire. For example, the photoelectric sensors are affected by baggy jogging clothes which pass through the light beam provided by the incandescent lamp causing false hits. Photoelectric sensors are also susceptible to dust accumulation producing false hits. An observer standing adjacent the running surface can also produce a false hit upon accidentally touching the side rails and crossing the path of light. Additionally, the photoelectric sensors require alignment between a lamp, a reflector, and a receiver, which makes them difficult to manufacture and susceptible to malfunction with the slightest misalignment.
Electrostatic sensors are not accurate because they are affected by many different factors including the temperature and humidity conditions, the degree of particulate matter in the air, electromagnetic interference produced by the drive motor and the clothing worn by user. Therefore, it is possible that while a user is having problems keeping up with the belt speed, an electrostatic sensor can pick up particulate matter in the air and falsely register that the user is proximate the front of the treadmill, and subsequently accelerate the belt forcing the user to dismount the treadmill and possibly causing injury.
Ultrasonic sensors are not desirable because they are geared to detect the position of the user by sensing the torso of the user and they could produce false hits if the user raises their arms. Further, ultrasound sensors may not be as accurate as some users desire because adjusting the belt speed as a function of the posture of the user causes the belt to speed up or slow down by leaning forward or backward, even if the user is sustaining the same pace as the belt.